A significant tool in the food and chemical industries for improvement of operating efficiencies and reduction of environmentally problematic materials is the use of cross-flow filters to separate solids and semisolids from liquid media. Such devices are used for such things as recovery of spent sulfite liquor, "mud" removal from converted corn syrup, residue removal from modified starches, removal of biological contaminants from fructose corn syrup, removal of particles from caustic cleaning solutions, recovery of PVA from textile desizing processes, clarification of alcohol still bottoms and many more.
The filter elements for such filters are comprised of a plurality of porous tubular substrates having interconnected pores of a relatively large pore size. The upstream (inner) side of the tubular substrates have finer particles impregnated therein to a slight depth to form a layer having a higher degree of filtration than the unaltered tube wall. The finer particles are affixed within the pores of the tubular substrate by sintering. Such cross-flow filter elements and their manufacture are described in U.S. Pat. No. 4,888,114 to Gaddis et al. Filters of this type are often used in conjunction with a formed-in-place membrane extending over the impregnated surface by which solute/solution separations can be carried out.
In common with most filtration systems, the pores of the filtration media are subject to abrasion by the liquid being treated and to clogging by various organic materials separated from the treated slurries which are not carried through the filter with the permeate or out of the filter with the slurry concentrate. When fouling of the pores and damage to the filter medium becomes sufficiently serious to impede the efficiency of the filter, the filter element must be removed from service and the medium replaced or repaired so that the original pore characteristics are regained. To repair sintered metal oxide filter media by cleaning, redepositing additional metal oxide and firing the filter to sinter the metal oxide means that the equipment must not only be out of service for at least several days, but in some cases even weeks. For this reason, there is a substantial need for a method of rejuvenating the filtration efficiency of such altered substrate filters in place without the necessity of shutting the filter down for more than 2-3 hours.